1. Field of the Invention
The present invention relates to mullite-crystal based alumina silica sintered ceramics (this term is hereinafter simply referred to as sintered ceramics) that are excellent not only in bending strength at room temperature (this bending strength is hereinafter simply referred to as room-temperature strength) but also in bending strength at temperatures of 800.degree. C. or higher, specifically at a high temperature of 1,300.degree. C. (this bending strength is hereinafter simply referred to as hot strength) and which displays high absolute values of these two types of bending strength. The present invention also relates to a process for producing such sintered ceramics by the normal sintering method.
More specifically, the present invention relates to the mullite-crystal based sintered ceramics that are produced by first providing a chiefly amorphous starting powder that is composed of alumina and silica, calcining the powder to the crystalline state, shaping (molding) the calcined powder into a compact, and sintering the compact at atmospheric pressure. The resulting sintered ceramics are suitable for use in the manufacture of firing burner nozzles, parts of internal combustion engines, high-temperature jigs and in other applications that require room-temperature strengths of at least 300 MPa and hot strengths of at least 400 MPa. The present invention also relates to a process for producing such sintered ceramics.